1. Field of the Invention
The present invention relates to a semiconductor device having an SOI structure, i.e., Silicon On Insulator, and a method for producing the same. More particularly, it relates to a structure for improving the gate break down voltage in a MIS semiconductor device having an SOI structure and the method for producing the same.
2. Description of the Related Art
Recently, a semiconductor device having an SOI structure produced by the steps of forming a polycrystalline silicon layer on an insulating layer formed on a semiconductor substrate, single-crystallizing the polycrystalline silicon layer by a laser annealing process, etc., and forming a MIS transistor on the obtained single-crystallized semiconductor layer (Silicon on Insulator) was proposed, to obtain a high density and high break down voltage. In the MIS transistor having an SOI structure, insulation between a gate electrode and an SOI substrate is carried out merely by forming a thin gate insulating layer, and thus a gate breakdown voltage is likely to be lowered by partial defects in the gate insulating layer formed below the gate, so that the gate breakdown voltage is reduced.